RxJS - Mathematical Operator Reduce

In reduce operator, accumulator function is used on the input observable, and the accumulator function will return the accumulated value in the form of an observable, with an optional seed value passed to the accumulator function.

The reduce() function will take in 2 arguments, one accumulator function, and second is the seed value.

Syntax

reduce(accumulator_func, seeder?) : Observable

Parameters

accumulator_func − (optional). a function that is called on the source values from the observables.

seeder − ((optional) By default it is undefined. The initial value to considered for accumulation.

Return value

It will return an observable that will have a single accumulated value.

We will see some examples to see how the reduce operator works.

Example 1

import { from } from 'rxjs';
import { reduce } from 'rxjs/operators';

let items = [
   {item1: "A", price: 1000.00},
   {item2: "B", price: 850.00},
   {item2: "C", price: 200.00},
   {item2: "D", price: 150.00}
];
let final_val = from(items).pipe(reduce((acc, itemsdet) => acc+itemsdet.price, 0));
final_val.subscribe(x => console.log("Total Price is: "+x));

Output

Total Price is: 2200